The present invention relates to the field of motors, and specifically to fluid-powered linear motors with rotary pistons for drilling.
Downhole drills are used for oil drilling, geothermal drilling, and other deep earth penetration applications. Downhole drills include rotary and percussive drills. For nearly any drilling method, rotational energy must be transferred downhole in order to promote rock reduction. The drill bit may be rotated by an electric motor or fluid/hydraulic system. The rotating action can be produced either at the surface or near the drill bit. In addition to rotational cutting, drills may also be pressurized or mechanically actuated to force the drill bit to hammer against the rock/earth. Prior art rotation systems and methods are complex, require large form factors to create sufficient torque, and require a high degree of maintenance.
The most common method of downhole energy transfer is rigid drill pipe. The drill pipe is rotated from the surface, with drilling joints added for tripping (moving in and out of the hole). For this type of system, the entire drill string rotates. Typically, a rotary table system or a top drive is used to drive the drill string. Although it is well suited for vertical drilling, it has limited applications in directional drilling because the drill string curvature and thrust loads generate additional torque that the surface based motor must overcome and drill pipe survive.
Downhole techniques used to generate rotation such as positive displacement motors (PDMs) are limited in their temperature range due to the use of elastomers. Energy resources like geothermal and deep oil and gas wells lie in hot (160° C.-300° C.), and often hard rock. The high-temperatures limit the use of PDMs in those environments. Additionally, while PDM motors are used for the vast majority of directional drilling operations, they introduce significant lateral vibration to the drilling assembly as the multi-lobed helical rotor comprising the power section undergoes nutation within the motor housing to generate rotor rotation. This lateral vibration is detrimental to both hardware life and directional drilling operations.
U.S. Pat. No. 9,447,798 discloses a motor that includes a module assembly incorporating an axially-cycled piston. The piston axial motion is torque coupled to convert the axial motion into rotary motion. The method does not require elastomers for operation and the rotor operates concentrically thereby not inducing lateral vibration. A modular fluid powered linear piston motor with harmonic coupling is described in U.S. patent application Ser. No. 15/090,282 filed Apr. 4, 2016, entitled “Modular Fluid Powered Linear Piston Motors with Harmonic Coupling”, and includes a drive train to convert reciprocating motion from a piston into rotary motion in an output shaft. Rotation is accomplished with roller balls captured between an inner race and a drive liner to facilitate rotation between a rotor and a stator. These roller balls must operate with low friction to enable smooth operation of the motor. Additionally, they must operate under a high contact load as they are in the preloaded and active load path to transmit torque to the output rotor. Finally, they must potentially operate with an abrasive drilling fluid under the rigors of high ambient temperatures and high friction conditions.
The limitations of these configurations are: 1) many pistons are required to generate the requisite torque to drive a drill bit downhole, and 2) any particulates in the drilling fluid would potentially settle out on the upper surfaces of the piston and eventually restrict operation.
What is needed are systems and/or methods that overcome one or more of these limitations or provides other advantageous features.
Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.